The invention relates to the tensioning of belts, drive chains and the like. More particularly, the invention relates to a tensioner for controlling tension in a drive belt of an extrusion apparatus.
FIG. 1 shows a prior art extruder 20. The extruder has a hopper 22 for storing and dispensing a feedstock such as a pelletized plastic 24. The base of the hopper is placed in communication with an inlet of a screw assembly 26 which contains a screw (not shown), compacts the feedstock 24 and drives it through a die 28 proximate an outlet 30 of the extruder. The screw rotates about a central extrusion axis 200. Power to drive the drive screw is provided by an electric motor 32 supported on a base 34. The drive screw is connected to a transmission 36 which has an input pulley or sheave 38 mounted on an input shaft 40 rotatable about a horizontal input pulley axis 202 parallel to the extrusion axis. The motor 32 has a drive shaft 42 and a drive pulley or sheave 44 mounted thereon. The pulley 44 and shaft 42 are rotatable by the motor about a horizontal drive pulley axis 204 parallel to the axes 200 and 202. A v-belt 46 overwraps the pulleys 38 and 44 to transmit torque and rotation from the motor to the transmission so as to drive the drive screw.
The motor is attached to a motor mounting plate 50. Four threaded studs 52 (of which two are shown) extend upward from the base 34 to carry the motor. Specifically, each stud bears lower and upper nuts 54 and 56 respectively. The underside of the plate 50 is supported on the upper surfaces of the lower nuts 54 and the upper surface of the plate 50 is engaged to the undersides of the upper nuts 56 to prevent upward movement of the plate 50 and motor 32.
To increase tension in the belt 46, a user sequentially applies a wrench (not shown) to each lower nut 54 rotating the nut to lower it along the associated stud 52. The motor and plate will typically descend along with the nuts 54 whereupon the user may apply the wrench sequentially to the upper nuts 56 to lower the nuts 56 to tighten them against the plate 50. If necessary, where a relatively high tension in the belt is required, the plate 50 will remain engaged to the upper nuts 56 when the lower nuts 54 are lowered. The tightening of the nuts 56 drives the plate and motor downward into engagement with the nuts 54 and, thereby, increases tension in the belt 46.
Decreasing tension in the belt 46 is accomplished in the reverse of the foregoing process. Tensioning and detensioning of the belt are not merely performed during operation of the extruder but, rather, are also performed to facilitate belt replacement or change out of the pulleys 38 and 44 to alter the drive ratio between the motor 32 and the transmission 36. In addition to the expenditure of user effort, the time required for the sequential turning of the various nuts 54 and 56 imposes significant downtime for the extruder.
Accordingly, there is a need for belt tensioning system which provides enhanced ease and speed of use, reducing user effort and extruder downtime.